It is known in the art to produce fluoroelastomeric articles by curing fluoropolymer compositions. U.S. Pat. No. 3,876,654 to Pattison discloses such compositions, processes for producing such articles, and such articles.
The present invention is an improvement over the composition and process taught in the Pattison patent. It has now been found that a faster cure can be obtained by use of the composition of the invention, or if desired the composition can be cured at about the same rate as that taught in Pattison, but the resulting product will have improved compression set and reduced water swell.
The curable fluoropolymer composition taught by Pattison contains:
1. A copolymer of vinylidene fluoride and at least one other fluorinated monomer, [Example of such other monomers include hexafluoropropylene, and mixtures of hexafluoropropylene and tetrafluoroethylene],
2. A quaternary phosphonium compound which acts as a vulcanization accelerator,
3. A divalent metal oxide or hydroxide or mixtures of said oxides or hydroxides with salts of weak acids, and
4. A crosslinking agent.
It has now been found that the Pattison composition is improved by the addition of 0.2 to 4 parts by weight, based on 100 parts of the fluoropolymer of a polyol selected from the class consisting of pentaerythritol, dipentaerythritol, trimethylol propane, and 2,2-dimethyl-1,3-propanediol. The polyol acts to accelerate the rate of cure, or if desired the polyol may replace a portion of the quaternary phosphonium compound accelerator and in doing so yields a composition that cures at about the same rate but results in a cured product having improved resistance to compression set. Finally the use of the polyol allows for the use of less metal oxide or hydroxide, and such a composition when cured has improved resistance to steam or boiling water--that is, it does not swell as much as the composition containing more divalent metal oxide or hydroxide.